Might be a my fault one-off. On the OnePlus 7t T-Mobile version I couldn't get 4G / Network access working with LOS 18.1. Will need to try again in a few days.
I have the same problem. Just updated to the latest update, and now I can't get any cellphone reception.
I tried to reset network, but can't reset cellphone settings since it can't fint my sim card. It just keep toggling on/off upp in the right corner